Hitherto, a plate heat exchanger is proposed as one of a heat exchanger for heat exchange between a first fluid medium and a second fluid medium.
A plate heat exchanger includes a plurality of heat transfer plates. The heat transfer plates each are formed by press molding a metal plate and have a plurality of recessed strips and projected strips formed on each of both front and back sides and at least four openings extending through both the front and back sides.
In the plate heat exchanger, the heat transfer plates having the above configuration are stacked to each other so as to form alternately a first flow channel for circulation of a first fluid medium and a second flow channel for circulation of a second fluid medium with each heat transfer plate therebetween.
In the plate heat exchanger, two of four openings of each heat transfer plate each are aligned with each of the corresponding two openings of each adjacent heat transfer plate to form a pair of first connection flow channels for allowing a first fluid medium to flow into and out of the first flow channel, and the remaining two openings of each heat transfer plate each are aligned with each of the corresponding two openings of each adjacent heat transfer plate to form a pair of second connection flow channels for allowing the second fluid medium to flow into and out of the second flow channel.
With the above configuration, the plate heat exchanger is configured such that the first fluid medium which has flown into the first flow channel from one of the first connection flow channels is discharged into the other of the first connection flow channels, while at the same time the second fluid medium which has flown into the second flow channel from the one of the second connection flow channels is discharged into the other of the second connection flow channels. Thus, the plate heat exchanger performs heat exchange between the first fluid medium which circulates through the first flow channel and the second fluid medium which circulates through the second flow channel via the heat transfer plates.
Meanwhile, as the plate heat exchanger of this type, there is a plate heat exchanger of a gasket type that includes gaskets each interposed between each adjacent heat transfer plates to define flow channels for circulation of fluid mediums (a first flow channel and a second flow channel).
A plurality of the heat transfer plates of the plate heat exchanger of a gasket type each form a gasket fitting groove for fittingly receiving a gasket. A more specific description is given herein. Each heat transfer plate has one side facing the adjacent heat transfer plate, and the other side opposite to the one side. Each heat transfer plate has an annular gasket fitting groove on any one of the one side and the other side, which surrounds all of the two openings, and annular gasket fitting grooves on at least one of the one side and the other side, which respectively surround the two openings other than the aforesaid two openings (the remaining two openings).
With the above configuration, in the plate heat exchanger of a gasket type, gaskets are mounted (fitted) in the respective gasket fitting grooves, and the plurality of the heat transfer plates are stacked to each other. Whereby, the respective gaskets seal the interface between each adjacent heat transfer plates, and define flow channels for circulation of fluid mediums (a first flow channel and a second flow channel) and connection flow channels for allowing the fluid mediums to flow into and out of the flow channels (a first connection flow channel and a second connection flow channel) between each adjacent heat transfer plates (see Patent Literature 1, for example).
Meanwhile, in the plate heat exchanger of a gasket type, a recessed strip formed on each heat transfer plate is formed to intersect with a gasket fitting groove in some cases.
In this case, the recessed strip is continuous with the gasket fitting groove to thereby partially open the gasket fitting groove. A more specific description is given herein. The gasket fitting groove is defined by a pair of vertical walls that are arranged with a distance from each other in a direction orthogonal to the groove longitudinal direction while facing each other. Accordingly, when the recessed strip is formed to intersect with the gasket fitting groove (when the recessed strip is formed to be continuous with the gasket fitting groove), the recessed strip causes the gasket fitting groove to open through its vertical wall.
Therefore, the gaskets defining the flow channels (the first flow channel and the second flow channel) are partially deformed toward (partially pressed into) the corresponding recessed strips due to the thermal expansion effected by the influences of heat in some cases. When the gaskets are partially deformed in this manner, a relative positional relationship between the gaskets and the heat transfer plates cannot be kept constant, which prevents the sealing performance of the flow channels (the first flow channel and the second flow channel) (the sealing performance between each adjacent heat transfer plates) from being maintained and hence may cause a fluid leakage.